CN109783865B - Method for solving unit length parameter matrix of three-core power line - Google Patents
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Abstract
The invention provides a method for solving a unit length parameter matrix of a three-core power line. Because the unit length parameter matrix element of the three-core power line cannot directly obtain an accurate value, an initial value of the unit length parameter can be obtained based on an electromagnetic simulation method, and because more parameters are directly corrected, each parameter can influence channel measurement results in multiple modes, a parameter correction method based on a mode field is provided, so that correction of each parameter can be independently completed. Based on a phase-mode transformation method, decoupling a unit length parameter matrix of a three-core power line into common mode and differential mode parameters, and carrying out linear correction on the unit length parameter of a mode by measuring open-circuit impedance under two modes on the basis of electromagnetic simulation to finally obtain an accurate value of the unit length parameter matrix.
Description
Technical Field
The invention relates to the field of communication, in particular to a three-core power line unit length parameter matrix solving method.
Background
For a three-core power cable, a Multiple-Input Multiple-Output (MIMO) transmission mode is adopted, so that the channel capacity can be further improved. In the technical field of MIMO-PLC, a great deal of test and research work is carried out by students at home and abroad, the coupling effect between core wires can be accurately analyzed based on a bottom-up method, the method can be used for predicting channel characteristics, and the method calculates channel transmission and impedance characteristics based on a transmission line theory and a network topology structure, and has the difficulty in accurately acquiring a parameter matrix of a unit length of a power line.
From the current related research work at home and abroad, the main acquisition method of the unit length parameter comprises the following steps: the approximate formula calculation method is based on a measurement method and an optimization method. The unit length parameter is calculated by adopting an approximate formula, and the calculation result and the measurement result have larger errors due to the fact that the influence of the proximity effect and the insulating medium cannot be accurately calculated. When the unit length parameter is calculated based on the measurement method, the extreme values of the open circuit input impedance and the short circuit input impedance are alternately changed in the frequency domain, and the result of multiplication or division between the two is subject to the accuracy of the measurement result, so that the calculated unit length parameter has larger error. When the unit length parameter is calculated based on the optimization method, the minimum error based on all the parameters is used as an optimization target, so that the calculation complexity is high. The unit length parameter is obtained based on the electromagnetic simulation method, the influence of the proximity effect is considered, and the accurate unit length resistance value and inductance value can be obtained. However, since the high frequency characteristics of different power line insulating materials are often different, accurate capacitance values and conductance values per unit length are still not obtained.
At present, the problem of accurately acquiring the unit length parameter matrix of the three-core power line is not solved well.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for solving a unit length parameter matrix of a three-core power line.
The embodiment of the invention provides the following technical scheme:
a three-core power line unit length parameter matrix solving method comprises the following steps:
extracting a unit length resistance matrix R based on an electromagnetic field simulation tool according to the radius and the distance of each conductor of the three-core power line to be detected and the cross section size of surrounding insulating medium 0 Inductance matrix L 0 Capacitor matrix C 0 Conductivity matrix G 0 Wherein, the method comprises the steps of, wherein,
the 4 parameter matrix per unit length has 8 parameters, wherein: g m And C m Is a negative number;
assuming the angular frequency of the signal is omega, the series impedance matrix per unit length is Z 0 ＝R 0 +jωL 0 The parallel admittance matrix is Y 0 ＝G 0 +jωC 0 Calculating a phase-mode transformation matrix T, and decomposing the phase-mode transformation matrix T into two mutually independent propagation modes of a differential mode and a common mode in a mode domain by utilizing the phase-mode transformation matrix T, wherein for the differential mode, 4 unit length parameters are usedThe numbers are R respectively s -R m 、L s -L m 、G s -G m And C s -C m For the common mode, the parameters of 4 unit lengths are R s +R m 、L s +L m 、G s +G m And C s +C m Calculating to obtain the differential mode and common mode input impedance of the starting end under the tail end open circuit;
obtaining common mode and differential mode input impedance of a starting end under an open end by a measuring method;
solving the capacitance C and the conductance G of the unit length of the common mode and the differential mode by using a linear correction method based on the calculated input impedance of the differential mode and the common mode of the starting end under the open end and the measured input impedance of the differential mode and the common mode of the starting end under the open end, and obtaining the capacitance C and the conductance G of the unit length after the correction of the common mode and the differential mode;
and obtaining an actual unit length parameter matrix according to the obtained unit length capacitance C and the conductance G after the common mode and differential mode correction.
The method for obtaining the common mode and differential mode input impedance of the starting end under the open end by using a measuring method specifically comprises the following steps:
in order to measure common mode impedance, core wires at two sides of the initial end of a three-core power line to be measured are short-circuited, a port 1 of a network analyzer is connected between two side cores and a middle core, the tail end of a cable is open-circuited, and S is obtained according to measurement 11 The measured common mode input impedance of the starting end under the open end is:
in order to measure the differential mode impedance, a port 1 of the network analyzer is connected between core conductors at two sides of the initial end of a three-core power line to be measured, the tail end of the cable is opened, and the S 'is obtained according to measurement' 11 The measured differential mode input impedance at the beginning and at the end under the open circuit is:
the method for solving the capacitance C and the conductance G of the unit length of the common mode and the differential mode by using a linear correction method based on the calculated input impedance of the differential mode and the common mode of the initial end under the open end and the measured input impedance of the differential mode and the common mode of the initial end under the open end to obtain the capacitance C and the conductance G of the unit length after the correction of the common mode and the differential mode specifically comprises the following steps:
setting the conductance G=0, solving the capacitance C in unit length by using a linear correction method to obtain the value of the capacitance C in unit length after correction, and correcting the capacitance C in unit length by using the step according to the initial values of the parameters in unit length of the differential mode and the common mode to obtain the values of the capacitance C in unit length after the differential mode and the common mode correction respectively;
after the value of the corrected capacitance C in unit length is obtained, the linear correction method is utilized to solve the conductance G in unit length, the value of the corrected conductance G in unit length is obtained, and by utilizing the step, the correction of G is respectively carried out for the initial value of the parameters in unit length of the differential mode and the common mode, and the values of the conductance G in unit length after the differential mode and the common mode correction are respectively obtained.
The method comprises the steps of setting a conductance G=0, solving a capacitance C in a unit length by using a linear correction method to obtain a corrected capacitance C in the unit length, correcting the capacitance C for initial values of parameters in the unit length of a differential mode and a common mode respectively, and obtaining the capacitance C in the unit length after the differential mode and the common mode respectively, wherein the method specifically comprises the following steps:
let the actual capacitance
Wherein: f is the frequency, f end The maximum frequency value of electromagnetic simulation, m and n are undetermined coefficients;
according to the errors of the previous periods in the frequency domain, correcting m to enable the calculated differential mode input impedance of the end open circuit lower start end and the measured oscillation period of the differential mode input impedance of the end open circuit lower start end to be well matched, if the matching degree is not ideal in a high frequency band, correcting n to enable the whole frequency band to meet the precision requirement, and enabling the calculated differential mode input impedance of the end open circuit lower start end and the measured differential mode input impedance oscillation period of the end open circuit lower start end to be basically consistent through linear correction to obtain the value of the capacitance C in unit length after differential mode correction;
according to the errors of the previous periods in the frequency domain, correcting m to enable the calculated common-mode input impedance of the starting end under the tail end open circuit to be well matched with the measured oscillation period of the common-mode input impedance of the starting end under the tail end open circuit, if the matching degree is not ideal in a high frequency band, correcting n to enable the whole frequency band to meet the precision requirement, and enabling the calculated common-mode input impedance of the starting end under the tail end open circuit in the whole frequency band to be basically consistent with the measured oscillation period of the common-mode input impedance of the starting end under the tail end open circuit through linear correction to obtain the value of the capacitance C in unit length after common-mode correction.
After obtaining the value of the corrected capacitance C of the unit length, the linear correction method is used to solve the conductance G of the unit length to obtain the value of the corrected conductance G of the unit length, and the step is used to correct the parameters of the unit length of the differential mode and the common mode to obtain the values of the conductance G of the unit length after the differential mode and the common mode correction, respectively, and specifically includes:
adjusting the numerical value of tan (theta) to enable the calculated differential mode input impedance of the tail end and the beginning end under the open circuit to be basically consistent with the measured oscillation amplitude of the differential mode input impedance of the tail end and the beginning end under the open circuit, and obtaining the numerical value of the conductance G in unit length after differential mode correction;
and (3) adjusting the value of tan (theta) to enable the calculated common-mode input impedance of the starting end under the tail end open circuit to be basically consistent with the measured oscillation amplitude of the common-mode input impedance of the starting end under the tail end open circuit, and obtaining the value of the conductance G of the unit length after common-mode correction.
Compared with the prior art, the technical scheme has the following advantages:
the method provided by the embodiment of the invention provides a three-core power line unit length parameter matrix solving method, which can obtain an initial value of unit length parameters based on an electromagnetic simulation method, and each parameter can influence channel measurement results in various modes because of more parameters which are directly corrected. Based on a phase-mode transformation method, decoupling a unit length parameter matrix of a three-core power line into common mode and differential mode parameters, and carrying out linear correction on the unit length parameter of a mode by measuring open-circuit impedance under two modes on the basis of electromagnetic simulation to finally obtain an accurate value of the unit length parameter matrix.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a method for solving a unit length parameter matrix of a three-core power line;
FIG. 2 is a schematic cross-sectional view of a three-core power line;
FIG. 3 is a schematic diagram of two mutually independent propagation modes of a differential mode and a common mode;
fig. 4 is a schematic diagram showing comparison between the calculation result and the measurement result of the differential mode and the common mode input impedance of the starting end and the starting end under the open end after the parameter correction.
Detailed Description
As described in the background art, how to obtain an accurate parameter matrix of unit length of the three-core cable is a technical problem that needs to be solved urgently by those skilled in the art.
In order to solve the technical problems, the invention provides a method for solving a unit length parameter matrix of a three-core power line, and the core idea of the invention is that the unit length parameter matrix element of the three-core power line can not directly obtain an accurate value, an initial value of the unit length parameter can be obtained based on an electromagnetic simulation method, and each parameter can influence channel measurement results in various modes due to more parameters which are directly corrected, so that the correction of each parameter can be independently completed. Based on a phase-mode transformation method, decoupling a unit length parameter matrix of a three-core power line into common mode and differential mode parameters, and carrying out linear correction on the unit length parameter of a mode by measuring open-circuit impedance under two modes on the basis of electromagnetic simulation to finally obtain an accurate value of the unit length parameter matrix.
The open circuit impedance is the input impedance of the starting end under the end open circuit.
First, a capacitor C and a conductance G are described, specifically as follows:
in practice, PVC and other materials are often used for the insulating layer and the sheath in the medium-voltage power line, and the dielectric constant is affected by the material characteristics, the processing technology and the filler and is a weak correlation function of frequency. The conductance in parallel with the capacitance is also related to the insulating material. The actual power line insulation material mainly considers the insulation performance at 50Hz, and as the frequency increases, more leakage current formed by dipole motion flows in the medium. In order to fully describe these two electrical properties of the insulating material, it is necessary to introduce a complex dielectric constant
ε r ＝ε′ r -iε″ r
Wherein ε' r For a dielectric constant related to capacitance value ε r Representing the loss-related portion.
In practice, the conductance G is described by the loss tangent tan (θ)
G＝ωtan(θ)C
Where ω is the angular frequency of the signal, ω=2pi f, f is the frequency, and f is in Hz.
Fig. 1 is a schematic diagram of a three-core power line unit length parameter matrix solving method, the method includes:
step 101: according to the radius and the distance of each conductor of the three-core power line to be testedAnd the cross-sectional dimensions of the surrounding insulating medium, extracting the resistive matrix R per unit length based on the electromagnetic field simulation tool 0 Inductance matrix L 0 Capacitor matrix C 0 Conductivity matrix G 0 ，
Wherein,,
the 4 parameter matrix per unit length has 8 parameters, wherein: g m And C m Is a negative number of the number,
the three-core power line to be tested is a symmetrical three-core power line.
Taking the three-core power line of fig. 2 as an example, and taking the middle conductor as a reference ground, the cable has a symmetrical structure, and the three-core wires form a 2+1 transmission line system, so that the three-core conductors are marked as a, b and c in sequence from left to right for convenience of description. In electromagnetic simulation, the dielectric constant epsilon 'of the PVC is preset according to the typical characteristics of the PVC' r The loss tangent tan (θ) was 3, which was 0.04.
The electromagnetic field simulation tool may be any of a variety of electromagnetic field simulation tools, such as ANSYS, and the present invention is not limited to this, and the electromagnetic field simulation tool of ANSYS may be used to extract the resistance matrix and the inductance matrix per unit length. Because the resistance and inductance values of unit length are not affected by the parameters of the insulating medium, the resistance matrix and the inductance matrix obtained based on electromagnetic simulation are accurate values, and the conductance matrix and the capacitance matrix need to be corrected.
Step 102: assuming the angular frequency of the signal is omega, the series impedance matrix per unit length is Z 0 ＝R 0 +jωL 0 The parallel admittance matrix is Y 0 ＝G 0 +jωC 0 For a three-core power line to be tested, calculating a phase-mode transformation matrix T, carrying out phase-mode transformation by using the phase-mode transformation matrix, decomposing the phase-mode transformation matrix into two mutually independent propagation modes of a differential mode and a common mode in a mode domain, and calculating to obtain the differential mode and common mode input impedance of a starting end and an end under an open circuit.
The specific process is as follows:
setting a signalIs ω, the series impedance matrix per unit length is Z 0 ＝R 0 +jωL 0 The parallel admittance matrix is Y 0 ＝G 0 +jωC 0 I.e.
The phase-mode transformation matrix T is calculated as follows:
through phase-mode transformation
In the mode domain, the two propagation modes, i.e. the differential mode and the common mode, can be separated from each other, for example, as shown in fig. 3.
Wherein, the differential mode component propagates through conductors on two sides, and the currents of the two conductors are equal in magnitude and opposite in direction. The common mode component flows back through the middle reference conductor, and the currents of the conductors at the two sides are equal in magnitude and direction.
For the differential mode, the parameters of the 4 unit lengths are R s -R m 、L s -L m 、G s -G m And C s -C m The method comprises the steps of carrying out a first treatment on the surface of the For the common mode, the parameters of the 4 unit lengths are R s +R m 、L s +L m 、G s +G m And C s +C m . The two sets of parameters form two mutually independent double-conductor transmission line systems, and the actual parameter matrix of the unit length can be obtained by reversely calculating after accurately solving the two sets of parameters of the unit length.
Since the mode-domain input impedance of a section of uniform cable presents the typical oscillation characteristic of a two-conductor transmission line, a simple linear fitting method can be adopted to carry out parameter correction on the basis. The following describes a parameter correction method for a two-conductor transmission line system, which is applicable to both the differential mode and the common mode cases. In the correction process, the influence analysis of the unit length parameter is carried out based on the low-loss characteristic of the power line, and the influence of the unit length capacitor and the electric conductance on the input impedance of the starting end under the open end is separated, namely the unit length capacitor C and the electric conductance G are corrected respectively, so that the process of solving the unit length parameter is simplified.
And setting the parameters of unit length of the uniform transmission line as R, L, G and C respectively, and further obtaining the secondary parameters of the transmission line. Wherein the propagation constant is
Characteristic impedance of
Let the length of the transmission line be l b The input impedance of the starting end under the end open circuit is
In the frequency range below 15MHz, the general low-loss line condition is satisfied by the low-voltage power cable: r < < ωL and G < < ωC. Can obtain corresponding approximate results of
Then calculateInput impedance Z to the end of the open circuit ino Can be simplified into
And substituting 4 unit length parameters of the differential mode and the common mode into the above formula to obtain the calculation results of the differential mode and the common mode input impedance of the starting end and the starting end under the open end.
Step 103: the common mode and differential mode input impedance of the starting end and the starting end under the open end is obtained by a measuring method, which concretely comprises the following steps:
in order to measure common mode impedance, core wires a and c at the two sides of the initial end of a three-core power line to be measured are short-circuited, a port 1 of a network analyzer is connected between two side cores and a middle core b, the tail end of a cable is open-circuited, and S is obtained according to measurement 11 The measured common mode input impedance of the starting end under the open end is:
in order to measure the differential mode impedance, a port 1 of the network analyzer is connected between an a core conductor and a c core conductor at the initial end of a three-core power line to be measured, the tail end of the cable is opened, and the S 'is obtained according to measurement' 11 The measured differential mode input impedance at the beginning and at the end under the open circuit is:
step 104: and solving the capacitance C and the conductance G of the unit length of the common mode and the differential mode by using a linear correction method based on the calculated input impedance of the differential mode and the common mode of the starting end under the open end and the measured input impedance of the differential mode and the common mode of the starting end under the open end, and obtaining the capacitance C and the conductance G of the unit length after the correction of the common mode and the differential mode.
Step 1041: setting the conductance G=0, solving the capacitance C in unit length by using a linear correction method to obtain corrected capacitance C in unit length, and correcting the capacitance C in unit length by using the step according to the initial values of the parameters in unit length of the differential mode and the common mode to obtain the values of the capacitance C in unit length after the differential mode and the common mode correction respectively;
the specific process of step 1041 includes:
let the actual capacitance
Wherein: f is the frequency, f end Maximum frequency value of electromagnetic simulation, which can be set by a user, e.g. f end =15 mhz, m and n are undetermined coefficients.
According to the errors of the previous periods in the frequency domain, correcting m to enable the calculated differential mode input impedance of the end open circuit lower start end and the measured oscillation period of the differential mode input impedance of the end open circuit lower start end to be well matched, if the matching degree is not ideal in a high frequency band, correcting n to enable the whole frequency band to meet the precision requirement, and enabling the calculated differential mode input impedance of the end open circuit lower start end and the measured differential mode input impedance oscillation period of the end open circuit lower start end to be basically consistent through linear correction to obtain the value of the capacitance C in unit length after differential mode correction;
according to the errors of the previous periods in the frequency domain, correcting m to enable the calculated common-mode input impedance of the starting end under the tail end open circuit to be well matched with the measured oscillation period of the common-mode input impedance of the starting end under the tail end open circuit, if the matching degree is not ideal in a high frequency band, correcting n to enable the whole frequency band to meet the precision requirement, and enabling the calculated common-mode input impedance of the starting end under the tail end open circuit in the whole frequency band to be basically consistent with the measured oscillation period of the common-mode input impedance of the starting end under the tail end open circuit through linear correction to obtain the value of the capacitance C in unit length after common-mode correction.
When solving the capacitance C of unit length, it sets tan (θ) =0, i.e. sets conductance g=0, ignores conductance G first, and separates the influence of capacitance C of unit length and conductance on the input impedance of the start end under the open end, i.e. corrects capacitance C of unit length and conductance G, respectively, so as to simplify the process of solving parameters of unit length.
In the frequency domain, Z ino Is set in the oscillation period of (a)
Is the same by the primary parameter L, C and the line length l b And (5) determining. L and known length L obtained by electromagnetic simulation b And C is corrected to an accurate value by comparing the calculated input impedance of the starting end under the open end with the measured input impedance oscillation period of the starting end under the open end.
As the frequency changes, when
When Z is ino Peak value, when->
When Z is ino Is the valley. Z in both cases ino Is 0 deg., resistive. When->
When Z is ino ＝Z C The phase reaches an extreme value. Oscillation period of input impedance of the starting end under the end open circuit and +.>
Is the same by the primary parameter L, C and the line length l b And (5) determining. When l b It is known that L, after simulation, can be determined from Z ino Specific values of C are obtained. Z is Z ino The oscillation period of (2) is related to the product of L and C, and the input impedance average Z of the beginning end under the end open circuit C Is determined by the ratio of L and C. When the obtained C enables the oscillation period to coincide, the average value of the input impedance of the starting end under the tail end open circuit is enabled to have good coincidence degree, and therefore accuracy of L and C is further verified. That is, C only affects the oscillation period and average value of the input impedance of the starting end under the open end, and accordingly, C can be corrected to an accurate value to obtain a corrected unitThe value of the length capacitance C.
Step 1042: after obtaining the value of the corrected capacitance C in unit length, solving the conductance G in unit length by using a linear correction method to obtain the value of the corrected conductance G in unit length, and correcting the conductance G in unit length by using the step according to the initial values of the parameters in unit length of the differential mode and the common mode to obtain the values of the conductance G in unit length after the differential mode and the common mode correction respectively, wherein the specific process comprises the following steps:
adjusting the numerical value of tan (theta) to enable the calculated differential mode input impedance of the tail end and the beginning end under the open circuit to be basically consistent with the measured oscillation amplitude of the differential mode input impedance of the tail end and the beginning end under the open circuit, and obtaining the numerical value of the conductance G in unit length after differential mode correction;
and (3) adjusting the value of tan (theta) to enable the calculated common-mode input impedance of the starting end under the tail end open circuit to be basically consistent with the measured oscillation amplitude of the common-mode input impedance of the starting end under the tail end open circuit, and obtaining the value of the conductance G of the unit length after common-mode correction.
Z ino The amplitude of oscillation damping is determined by
Determining, as the frequency increases, Z, affected by the R and G frequency variability ino And the oscillation amplitude of (c) becomes smaller. Since R is substantially proportional to the square root of frequency, G increases linearly with frequency. When the frequency is low, the value of G is small, and the influence of R is dominant, so that R can be verified according to the input impedance value of the low frequency band. In the high frequency band, G vs Z ino The influence of the oscillation amplitude becomes larger, according to Z ino The difference from the measured curve is corrected for the value of tan (θ) to obtain an accurate value of G.
Fig. 4 shows a comparison between the calculation result and the measurement result of the differential mode and the common mode input impedance of the starting end and the starting end under the open circuit after the parameter correction, and the matching degree of the mode value and the phase angle is good in both modes, which shows that the precision requirement of the model can be better met by adopting the linear correction, thereby avoiding the use of a more complex nonlinear method. After correction, the common mode parameter is R c 、L c 、G c And C c The differential mode parameter is R d 、L d 、G d And C d 。
Step 105: obtaining the actual parameter matrix of unit length according to the capacitance C and the conductance G of the unit length after the common mode and differential mode correction
Therefore, the method of the invention utilizes phase-mode transformation to decompose the unit length parameter matrix of the three-core power line into common mode and differential mode parameters, converts the three-conductor transmission line system into a double-conductor transmission line system, corrects the unit length capacitance and the conductance based on the open-circuit impedance characteristic of the double-conductor transmission line system, and avoids the complexity caused by simultaneous parameter correction. The accurate values of the resistance and the inductance in unit length are obtained based on electromagnetic simulation, reasonable estimated values of the capacitance and the conductance in unit length are obtained, and the estimated values are further corrected by combining the input impedance measurement result of the tail end and the starting end under the open circuit. Therefore, the invention combines two unit length parameter solving methods of electromagnetic simulation calculation and auxiliary measurement, and linear correction is carried out on the unit length capacitance and the conductance obtained by electromagnetic simulation by utilizing the auxiliary measurement result, thereby obtaining accurate unit length capacitance and conductance and avoiding the use of a complex nonlinear method.
According to the method, common mode impedance testing conditions and differential mode impedance testing conditions are respectively constructed at the initial ends of the three-core power lines through different core wire connection modes according to the numerical value of the phase-mode transformation matrix, and corresponding measurement is carried out.
In the correction process, the influence analysis of the parameters of the unit length is carried out based on the low-loss characteristic of the power line in the frequency band range of 30kHz-15MHz, the influence of the capacitance and the electric conduction of the unit length on the input impedance of the starting end under the open end is separated, namely the correction of the capacitance and the correction of the electric conduction of the unit length are carried out in sequence, the complexity caused by simultaneous correction of the capacitance and the electric conduction of the unit length is avoided, and the process of correcting and solving the parameters of the unit length is simplified. The method can effectively avoid the problem of data divergence caused by a direct measurement method, and can adopt a simple linear fitting method due to the small number of fitted parameters and small parameter correction range, thereby avoiding the complex calculation required by a nonlinear optimization method and the problem of easy non-causality.
In addition, the method of the invention takes the input impedance module value at the tail end and the beginning end under the open circuit and the measurement result of the phase angle as references to carry out unit length parameter solving and verification, and the method is simple and easy to implement and has high reliability.
The method disclosed by the invention is based on the numerical value of the phase-mode transformation matrix, and the modification of the unit length parameter is converted into the common mode and the differential mode, so that the complexity caused by the simultaneous modification of the parameters is avoided, and the solving step of the unit length parameter matrix is clear.
The method of the invention uses the parameter matrix of unit length obtained by electromagnetic simulation as an initial value to carry out parameter correction, so that the correction range is smaller, and an accurate value can be obtained by using a relatively simple linear method.
Compared with other methods, the method provided by the invention has the advantage that the accuracy of the parameter matrix per unit length obtained by the method is obviously improved.
The method disclosed by the invention utilizes the characteristic of symmetry of a common three-core power line structure, does not need to measure the dielectric constant of a cable insulating medium in advance, and has wide applicability in solving a parameter matrix of unit length.
In the present description, each part is described in a progressive manner, and each part is mainly described as different from other parts, and identical and similar parts between the parts are mutually referred.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (5)
1. The method for solving the parameter matrix of the unit length of the three-core power line is characterized by comprising the following steps of:
extracting a unit length resistance matrix R based on an electromagnetic field simulation tool according to the radius and the distance of each conductor of the three-core power line to be detected and the cross section size of surrounding insulating medium 0 Inductance matrix L 0 Capacitor matrix C 0 Conductivity matrix G 0 Wherein, the method comprises the steps of, wherein,
the 4 parameter matrix per unit length has 8 parameters, wherein: g m And C m Is a negative number;
assuming the angular frequency of the signal is omega, the series impedance matrix per unit length is Z 0 ＝R 0 +jωL 0 The parallel admittance matrix is Y 0 ＝G 0 +jωC 0 Calculating a phase-mode transformation matrix T, and decomposing the phase-mode transformation matrix T into two mutually independent propagation modes of a differential mode and a common mode in a mode domain by utilizing the phase-mode transformation matrix T, wherein for the differential mode, 4 unit length parameters are R respectively s -R m 、L s -L m 、G s -G m And C s -C m For the common mode, the parameters of 4 unit lengths are R s +R m 、L s +L m 、G s +G m And C s +C m Calculating to obtain the differential mode and common mode input impedance of the starting end under the tail end open circuit;
obtaining common mode and differential mode input impedance of a starting end under an open end by a measuring method;
solving the capacitance C and the conductance G of the unit length of the common mode and the differential mode by using a linear correction method based on the calculated input impedance of the differential mode and the common mode of the starting end under the open end and the measured input impedance of the differential mode and the common mode of the starting end under the open end, and obtaining the capacitance C and the conductance G of the unit length after the correction of the common mode and the differential mode;
and obtaining an actual unit length parameter matrix according to the obtained unit length capacitance C and the conductance G after the common mode and differential mode correction.
2. The method according to claim 1, characterized in that the common mode and differential mode input impedance of the start and the end under the open end is obtained by a measuring method, in particular comprising:
in order to measure common mode impedance, core wires at two sides of the initial end of a three-core power line to be measured are short-circuited, a port 1 of a network analyzer is connected between two side cores and a middle core, the tail end of a cable is open-circuited, and S is obtained according to measurement 11 The measured common mode input impedance of the starting end under the open end is:
in order to measure the differential mode impedance, a port 1 of the network analyzer is connected between core conductors at two sides of the initial end of a three-core power line to be measured, the tail end of the cable is opened, and S is obtained according to measurement 1 ' 1 The measured differential mode input impedance at the beginning and at the end under the open circuit is:
3. the method according to claim 1, wherein the solving the common mode and differential mode capacitance C and conductance G per unit length by using a linear correction method based on the calculated differential mode and common mode input impedance of the open-ended lower start end and the measured differential mode and common mode input impedance of the open-ended lower start end to obtain the common mode and differential mode corrected capacitance C and conductance G per unit length, specifically comprises:
setting the conductance G=0, solving the capacitance C in unit length by using a linear correction method to obtain the value of the capacitance C in unit length after correction, and correcting the capacitance C in unit length by using the step according to the initial values of the parameters in unit length of the differential mode and the common mode to obtain the values of the capacitance C in unit length after the differential mode and the common mode correction respectively;
after the value of the corrected capacitance C in unit length is obtained, the conductance G in unit length is solved by using a linear correction method to obtain the value of the corrected conductance G in unit length, and by using the step, the correction of G is carried out for the initial values of the parameters in unit length of the differential mode and the common mode respectively to obtain the values of the capacitance G in unit length after the differential mode and the common mode correction respectively.
4. A method according to claim 3, wherein the conductance g=0 is set, the capacitance C per unit length is solved by a linear correction method to obtain a corrected value of the capacitance C per unit length, and the correction of C is performed for the initial values of the parameters of the differential mode and the common mode to obtain the corrected values of the capacitance C per unit length, respectively, specifically comprising:
let the actual capacitance
Wherein: f is the frequency, f end The maximum frequency value of electromagnetic simulation, m and n are undetermined coefficients;
according to the errors of the previous periods in the frequency domain, correcting m to enable the calculated differential mode input impedance of the initial end under the end open circuit to coincide with the oscillation period of the measured differential mode input impedance of the initial end under the end open circuit, if the coincidence degree is not ideal in a high frequency band, correcting n to enable the whole frequency band to meet the precision requirement, and enabling the calculated differential mode input impedance of the initial end under the end open circuit in the whole frequency band to coincide with the measured differential mode input impedance oscillation period of the initial end under the end open circuit through linear correction to obtain the value of the capacitance C in unit length after differential mode correction;
according to the errors of the previous periods in the frequency domain, correcting m to enable the calculated common-mode input impedance of the starting end under the end open circuit to coincide with the measured oscillation period of the common-mode input impedance of the starting end under the end open circuit, if the coincidence degree is not ideal in the high frequency band, correcting n to enable the whole frequency band to meet the precision requirement, and enabling the calculated common-mode input impedance of the starting end under the end open circuit in the whole frequency band to coincide with the measured oscillation period of the common-mode input impedance of the starting end under the end open circuit through linear correction to obtain the value of the capacitance C in unit length after common-mode correction.
5. A method according to claim 3, wherein after obtaining the value of the corrected capacitance C per unit length, the conductance G per unit length is solved by a linear correction method to obtain the value of the corrected conductance G per unit length, and the correction of G is performed for the initial values of the parameters of the differential mode and the common mode to obtain the value of the capacitance G per unit length after the differential mode and the common mode correction, respectively, comprising:
adjusting the numerical value of tan (theta) to ensure that the calculated differential mode input impedance of the starting end under the tail end open circuit is consistent with the measured oscillation amplitude of the differential mode input impedance of the starting end under the tail end open circuit, and obtaining the numerical value of the conductance G of unit length after differential mode correction;
and (3) adjusting the value of tan (theta) to enable the calculated common-mode input impedance of the starting end under the tail end open circuit to be consistent with the measured oscillation amplitude of the common-mode input impedance of the starting end under the tail end open circuit, and obtaining the value of the conductance G of the unit length after common-mode correction.
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